Apparatus for controlling electrical power



Sept. ll, 1951 R. w. BROWN APPARATUS FOR CONTROLLING ELECTRICAL POWER Filed may 1o, 194e 3 Sheets-Sheet 1 W To NR mw. R.

Sept. ll, 1.951 R. w. BROWN 2,567,692

APPARATUS FOR CONTROLLING ELECTRICALPOWER Filed Hay ,10, 1948 3 Sheets-Sheet 2 /N VEN TOR l?. W ROW/V ay 3 Sheets-Sheet 5 MAM R. W. BROWN APPARATUS FOR CONTROLLING ELECTRICAL POWER Filed lay 10, 1948 Sept. ll, 1951 Y W Y um q MW E. mw r M .v s A m R n r. 0 l n A h l "um: I Il c ll "N\.Q\\ R o Y N a Qn Nr W SwN MN ma NM; n* l NQ s v .w n@ nu L35. r n 1 n-\ om s C. Qu f n n vn\ .m2 N\\( 4 3v |00 Qn N* .WN QM, .WAX

Patented Sept. 11, 1951 APPAR-ATUS FOR CONTROLLING ELECTRICAL POWER Raymond W. Brown, Oak Forest, lll., assigner to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application May 10, 1948, Serial No. 26,018

l 3 Claims.

This invention relates to control apparatus for electrical power and more particularly to an apparatus for regulating welding power.

In the continuous electrical roll welding of a metal strip to a metal base, it is necessary that the weld quality be closely controlled in order to prevent the manufacture of large amounts of poorly Welded material. Since it has been found that the power dissipated at the weld is a measure of the strength of the weld, it is desirable to maintain the weld power constant in order to insure uniformity of weld strength in welding a metal strip to a metal tape.

An object of this invention is to provide a new and efficient automatic apparatus for controlling the electrical power in a welding apparatus.

In accordance with one embodiment of this invention, a welding apparatus is provided wherein the variations of the power in the welding circuit are used to regulate the welding current by means of an electronic wattmeter circuit having its input connected to a welding circuit and its D. C. output connected through a D. C. amplifler to a phase control circuit for shifting the phase of the grid voltage applied to a current regulating electronic tube connected to the welding circuit.

A complete understanding of the invention may be had by referring to the following detailed description, taken in conjunction with the drawings, in which Fig. 1 is a diagram of the equivalent circuit of 1 a welding loop;

Fig. 2 is a block diagram illustrating one embodiment of the invention; and

Figs. 3A and 3B, which when considered together with Fig. 3A placed above Fig. 3B` cornprise a circuit diagram illustrating one embodiment of the invention.

The various equivalent resistances in a welding circuit for welding metal tape to metal strip are diagrammatically illustrated in the equivalent circuit shown in Fig. l. R-I represents the resistance from the electrode to the tape; R-2 the resistance of the tape; R-3 the resistance between the tape and the strip; R-I the resistance of the strip; R--5 the resistance between the strip and the other electrode; and R/-S and R-I the resistances of the leads to the electrodes. Although actual welding takes place only at R-3, the power dissipated in R-I, R-2, R-Ii and Rf-S is a part of the total power expended in the welding loop and is therefore closely related to the quality of the weld. The weld power will tend to vary due to any nonuniiormity in the tape or strip, corrosion or roughness at the surface ofl gram (Fig. 2) of the apparatus in which thev primary II) of a welding transformer II is connected to a source of electrical power I2 through a current controlling electronic tube circuit I3 having therein gas-lled tubes. The secondary I4 of the transformer II is connected, through leads 20 and 2 I, to a pair of electrodes 22 between which metal strip 23 and metal tape 24 are roll welded. A voltage proportional to the voltage across the electrodes 22 and a voltage proportional to the current in the weld circuit are fed to the input of an electronic wattmeter circuit 25 at 30 and 3|, respectively. The voltage proportional to the current in the welding circuit is obtained from the secondary 32 of a current transformer 33 having a primary 3l connected in series with the welding circuit between the electrodes and the secondary of the welding transformer.

The electronic wattmeter circuit 25 has a direct current output responsive to and changeable in accordance with changes in power in the welding circuit. 'I'he changes in the output of the wattmeter circuit 25 are amplified by a balanced direct current amplifier 35 whose output is connected to a phase-changing circuit 36 which regulates the phase of the voltage applied to the grids 4I and 40 of the electronic tubes in the tube circuit I3. If changes in the welding circuit cause the power at the weld to increase above a predetermined level. the D. C. output voltage of the wattmeter circuit 25 increases. This change is amplifled by the D. C. amplifier 35 and is then fed into the phase-changing circuit 3S and a phase change proportional to the change in power is then applied to the grid voltages of the tubes in the tube circuit I 3. This phase change is in such a direction as to cause these tubes to conduct for a lesser. portion of the cycle, thereby reducing the power flow to the welding transformer II. Thus, the power delivered to the weld is decreased to compensate for the increase detected hy the wattmeter circuit 25. Cnnverselv, when' the power decreases at the weld below the predetermined level, the tube circuit I3 is caused to conduct for a greater portion of the cycle and the power at the weld is increaeeri.

The first stage of the regulator is called a wattatcaeee 3 meter circuit 25 herein because it is responsive to the power'in the welding circuit and produces a D. C. output voltage proportional to the power ino the Welding circuit, which output is therefore a measure at all times of the power in the welding circuit. The wattmeter circuit 25 is provided with a pair of matched'electronic vacuum tubes 42 and 43, the tube 42 having an anode 44, a con-.

trol grid 50 and a cathode 5i and the tube 43 likewise being provided with an anode 52, a control grid 53 and a cathode 54. Both tubes 42 and 43 may be provided with supp-ressor and screen grids. The input circuit of tube 42 includes a resistor 60 connected to the input grid 50, 'and a resistor 6I connected to the resistor 60 Aand also to the cathode 5| through a bias voltage tap on a voltage divider 52 oi. a power supply 63. Similarly the input of the tube 43 includes a resistor 64 connected to the grid 53 and to the resistor 6| which is common to the inputs of both tubes.

The regulated power supply 63 provides anode, screen. bias and heater voltages for the tubes 42 and 43 and comprises a power transformer 65, a full-Wave rectier 10, a filter section 1|, a voltage regulator section 12, and a voltage divider 62. The negative end of the voltage divider 52 is connected to the resistor 6| and the positive end is connected to the anodes 44 and 52 through a variable balancing resistor 13 and dropping resistors 14 and 15, respectively. A variable tap 16 near the negative' end of the voltage divider 62 determines the grid bias on the tubes 42 and vacuum tube 8| and an associated regulated power supply 02 having .a power transformer 83, a full-wave rectifier 84, a'iilter section 90, a regulator section 9|, and a voltage divider 92. The tube 8| includes a pair of anodes 93 and 94, a pair of grids |00 and |0|, and a common cathode I 02. One side 18 of the wattmeter circuit output is connected to the grid |00 of the tube 8|. and the other side 19 is connected to the cathode |02 through a portion of the voltage divider 92 between variable taps |03 and |04, which portion of the voltage divider furnishes the bias voltage for the grid |00. A predetermined bias voltage is furnished to the grid IOI from a tap I|0 on the voltage divider 92. Voltages for the anodes 93 and 94 are obtained from the positive end of the voltage divider 92 which is connected to the anodes 93 and 94 through resistors and II2, respectively, the resistor ||2 preferably being variable.

The output of the amplier 35 at circuit points I I3 vand ||4 is the voltage drop across the resistors III and ||2 due to differential anode currents of the two triode sections in the tube-8|. A condenser I I5 is connected across the amplifier output to provide iiltering action, and a resistor i 6 across the output provides a stabilizing load.

The bias voltages on the grids |00 and |0I are 43 which operate on the curved portion of their eg-Ip curves. Screen Voltage for the tubes 42 and 43 is provided from a tap in the voltage regulator section 12 of the power supply.

The wattmeter circuit being a balanced arrangement, the resistors 60 and 64, preferably, have the samev resistance and the resistors 14 and 15 should be matched. Acondenser 80 connected betweenthe anodes 44 and 52 provides smoothing action to the output of the wattmeter circuit, and its capacitance value is a controlling factor in the response time of the apparatus.

An input voltage proportional to the voltage in the welding circuit is furnished to the wattmeter circuit 25 by applying across resistors 60 and 64 the voltage between the Welding leads 2| and 20, and a voltage proportional to the current in the Welding circuit is fed into the wattmeter circuit by connecting the secondary 32 of the current l transformer 33 across the resistor 6|. It is apparent that one of the wattmeter tubes will always receive in its input grid the sum of the input voltages across the resistors in its input, and the input grid of the other tube will receive the difference of the input voltages across the resistors in its input circuit. Differential anode currents throughthe resistors 14, 13 and 15 set up a D. C. potential difference between circuit points 18 and 19, which potential difference at any given time is a measure of power in the Weld circuit. The bias voltage for the grids 50 and 53 is adjusted at the voltage divider 62 so that when the power in the weld is at a predetermined desired level adjusted at the Avoltage divider 92 to so relate them that the bias voltage on the grid |0I will be nearly equal to the difference betwen the bias voltage on the grid |00 and the signal voltage on the grid |00 when the power at the weld is at the desired level.

As pointed out before, the object of the amplier is to amplify the changes in the D. C. output of the wattmeter circuit'at circuit points 18 and 19 in order to utilize these changes to control the phase of the voltages applied on the grids 40 and 4|. The output of the amplifier 35 is connected to two parallel phase-changing circuits |.1 and IIB, one (I I1) for controlling the phase of the grid voltage in a gas-lled electronic tube |I9, and the other I8) for controlling the phase of the voltage on the grid in a second gaslled tube |20. Both of the phase-changing circuits being similar, only the one designated as I|1 will be described.

The phase-changing circuit |I1 regulates the phase of the output of a bridge |2| having a pair of equal ratio resistance arms |22 and |23 and two adjacent reactive arms |24 and |25. Reactive arm |24 consists of a condenser |30, whereas the arm |25 is inductive and includes one of the windings |3| on an impedance transformer I 32. An alternating current is supplied to the input of the bridge |2I at |33 and |34 from the secondary of a transformer |40 whose primaryis connected to a source of alternating current. The output of the bridge at |4| and |42 supplies the grid voltage to the gas-filled electronic tube |I9, the point |42 of the bridge being connected to the grid 4I and the point |4I being connected to the cathode |44 of the tube II9. In the same manner a bridge |45 controlled by the phasechanging circuit II8 supplies the grid voltage on the grid 40 of the second gas-filled electronic tube |20, the two gas tubes being connected back-toback in series with the primary I0 of the welding transformer |I. By back-to-back relation, it is meant that the plate of one tube and the cathode of the other tube are tied together and viceversa. As shown in the drawing, the cathode |44 is tied to the anode |5I and the cathode |52 is tied to the anode |53. The back-to-back relaannees tion of the tubes permits current fiow through the primary of the welding transformer during both alter-nations of each cycle.

A center-tapped winding |54 on the impedance transformer |32 has its outer ends connected to the separate anodes |60 and ||6| of a double- .triode electronic vacuum tube |62 having a common cathode |63 connected to the center ltap of the winding |54 and also having a pair of control grids |64 and |65 normally connected through a switch |10 to one side ||3 of the output of the amplifier 35, the other side ||4 of the amplifier output being connected to the cathode |63 of the tube |62.

.It will be seen that the winding |54 and the tube |62 form a closed full-wave rectifier circuit receiving its anode voltage inductively from the winding |3| which may be likened to the primary of a power transformer in a conventional rectifier circuit. The anode currents of the two triode sections of the tube |62 which flow as direct currents through the winding |54 are regulated by and are dependent upon the potential on the grids |64 and |65 which in turn depends on the output of the amplifier 35. An amplitude change of the direct current in the winding |54 will, on the principle of the saturable reactor, change the inductive reactance of the winding Y |3|, thereby shifting the phase of the output voltage of the bridge |2|. As indicated before, a phase shift in this voltage changes the amount of average current conducted by the gas tube I9. The constants of the circuit elements should be selected and adj-usted so that when the power at the weld is at the desired level the output of the amplifier 35 will furnish an equilibrium voltage on the grids |64 and |65 that will permit the right amount of anode current to iiow through the winding |54 in order to effect the phase displacement of the voltage on the grid 4| that will permit the tube ||9 to conduct the desired amount of current to the welding transformer In order to stabilize the gas tubes ||9 and |20 and to protect them from undesirable transient currents, choke coils |1| and |12 are inserted in series with the anodes |5| and |53 and the tubes are shunted by condensers |13 and |14. Condensers |80 and |6| are connected between the grids and the cathodes of the tubes |20 and ||9, respectively, to stabilize operation.

A convenient method for initially setting the regulating apparatus for a particular desired weld power is to determine the necessary grid voltage on the grids of the double triodes in the phase-changing circuits that will cause the tubes ||9 and |20 to conduct the required amount of current to deliver thedesired weld power. This may be accomplished by feeding the grids of the double triodes in the phase-changing circuits with an independent variable voltage from a battery |62 instead of the output voltage from the ampliiier 35. Voltage from the battery |62 may be substituted for the output of the amplifier 35 by opening the circuit at |63 and closing the circuit at |84 with the switch |10 and, at the same time, closing a switch |90. This operation connects the positive side of the battery |62 to the cathodes of the double triodes in the phasechanging circuit and connects the grids of those tubes to the variable arm |9| of a potentiometer |92 connected across the battery |62. To provide an indication of the grid voltages on the grids of the double triodes in the phase-changing circuits a voltmeter |93 may be connected between the grids and the cathodes of the tubes by means of a switch |94. The grid voltage is then varied by moving the potentiometer arm |9| until the desired weld-power is being delivered in the welding circuit. When the required(I grid voltage is ascertained, the voltmeter |93 is connected across the output of the amplifier 35 by means of the switch |94 and the amplifier output is then adjusted by moving the tap |03 on the voltage divider 92 until the voltmeter |93 registers the required reference voltage ascertained by means of the substituted battery circuit, after which the output of the amplifier 35 is substituted for the battery |82 by opening the switch and operating the switch |10 to open the circuit at |84 and close the circuit at |63. These adjustments should be made when the desired weld power is being delivered, which power and its current and' voltage components may be checked by a wattmeter |95, an ammeter 200 and a voltmeter 20| properly connected to the welding circuit.

To insure stability, it is desirable that the tubes |9 and |20 conduct current during standby time when the welder is not in actual operation. For this purpose a certain amount of anode voltage is applied to the tubes ||9 and |20 by connecting the input bridge points |33 and |34 of the bridge |2| across the tubes ||9 and |20 through a power dissipating resistor 202 during the standby time. This is done by opening a relay operating circuit at a switch 203 during the standby time to deenergize and release a relay 204, thereby opening the circuit at 205 and closing the circuits at 2|0 and 2||. Obviously, the relay 204 must be energized and operated while the welding apparatus is in operation.

It is to be understood that the above-described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will ernbody the principles of-the invention and fall within the spirit and scope thereof.

What is claimed is:

1. Apparatus for regulating the electrical power delivered to a load comprising a pair of series connected resistors shunting said load, a current transformer having its primary winding in the load circuit, a third resistance element connected across the secondary of said current transformer, said third resistance element having one of its ends connected to the junction of said pair of resistors, Aa pair of electronic tubes each having an anode, a cathode, and a control grid. a source of balanced D. C. plate potential for said tubes, connectors connecting the control grids of said tubes across said series connected resistors and the cathodes of said tubes to the other end of said third resistance, to. thereby render said tubes conductive in response to vpower changes in the load circuit, an output circuit for said tubes including a load resistance connected across the plates of said tubes, a D. C. amplifier comprising a first and a second tube section each having an anode, a cathode and a control grid, a source of balanced D. C. plate potential for said tube sec'tions, a multi-tapped resistance connected across said last named source, means connecting the contol grid of the first of said tube sections to one side of said load resistance, means connecting the other side of said load resistance to the cathodes of said tube sections through a first tapped portion of said mul-l ti-tapped resistance, means connecting said other side of said load resistance to the control grid of said second tube section through a second tapped portion of said multi-tapped resistance, a plate resistance connected to each plate of said tube sections, a phase sensitive electronic device connected in series with said load to control the current thereto, said electronic device having an anode, a cathode and a control grid, means for applying a phase shiftable alternating current to said last named grid for controlling said electronic device, the last said means including a network having an inductive branch,l means for shifting the phase of said alternating current to said last named grid comprising a center tapped coil inductively coupled to said inductive branch, a third electronic tube section having an anode, a cathode and a grid, a fourth electronic tube section having an anode, a cathode and a grid, the anode of said third tube section being connected to one end of said center tapped coil, the anode of said fourth tube section being connected to the other end of said center tapped coils, the center tap of said coil being connected to the cathodes of said third and fourth tube sections, and the grids of said third :and fourth tube sections being coupled to the respective plates of said first and second tube sections whereby said third and fourth tube sections are rendered conductive in response to differential plate currents flowing in said rst and second tube section.

2. Apparatus for regulating the electrical power delivered to a load comprising a pair of series connected resistors shunting said load, a current transformer having its primary Winding in the load circuit, a third resistance element connected across the secondary of said current transformer, said third resistance element having one of its ends connected to the junction of said pair of resistors, a pair of electronic tubes each having an anode, a cathode and a control grid, a source of balanced D. C. plate potentials for said tubes, connectors connecting the control grids of said tubes across sa'id series connected resistors and the cathodes of said tubes to the other end of said third resistance, to thereby render said tubes conductive in response to power changes in the load circuit, an output circuit for said tubes including a load resistance connected across the plates of said tubes, an amplifier for amplifying the direct current `output of said tubes appearing across said load resistance, a. phase sensitive electronic device for controlling the current to said load, said electronic device having an anode, a cathode and a grid,`l`neans for applying alternating current to said grid comprising an impedance bridge having an alternating current input and an alternating current output connected to said grid, said bridge also having in one arm an' inductance coil and means responsive to the amplified direct current output of said amplifier for changing said inductance thereby to shift the phase of said bridge output in accordance with changes in said direct current output.

3. Apparatus for regulating the electrical power delivered to a load comprising'a pair of series connected resistors shunting said load, a current transformer having its primary winding in the load circuit, a third resistance element connected across the secondary of said current transformer, said third resistance element having one of its ends connected to the junction of said pair of resistors, a pair of electronic tubes each having an anode, a cathode and a control grid, a source of balanced D. C. plate potential for said tubes, connectors connecting the control grids of said tubes across said series connected resistors and the cathodes of said tubes to the other end of said third resistance, to thereby render said tubes conductive in response to power changes in the load circuit, an output circuit for said tubes including a load resistance connected lacross the plates of said tubes, a D. C.

amplier comprising a rst and a second tube section each having an anode, a cathode and a control grid, a source of balanced D. C. plate potential for said tube sections, means connecting the control grid of the first of said tube sections to one side of said load resistance, means including a first biasing resistance connecting the other side of said load resistance to the cathodes of said tube sections, means including a second biasing resistance connecting said other side of said load resistance to the control grid of said second tube section, a plate resistance connected to each plate of said tube sections, a phase sensitive electronic device connected in series Iwith said load to control the current thereto, said electronic device having an anode, a. cathode and a control grid, means for applying a phase shiftable alternating current'to said grid for controlling said electronic device, the last, said'means including a network having an inductive branch, means for shifting the phase of said alternating current to said grid comprising a center tapped coil-inductively coupled to said inductive branch, a third electronic tube section having an anode, a cathode and a grid, a fourth electronic tube section having an anode, a cathode and a grid, the anode of said third grid section being connected to one end of said center tapped coil, the anode of said fourth tube section being connected to the other end of said center tapped coil, the center tap of said coil being connected to the cathode of said third and fourth tube sections and the grids of said third and fourth tube sections being coupled to the respective plates of saidl first and second tube sections whereby said Vthird and fourth tube sections are rendered conductive in response to differential plate currents flowing in said first and second tube sections.'

RAYMOND W. BROWN.`

REFERENCES CITED The following references are of record in the iile of this patent: 

